Half began a supervised exercise program that reiterated the
Norwegian researchers’ former routine. After briefly warming up, these
volunteers ran on a treadmill at 90 percent of their maximal heart rate —
a tiring pace, says Dr. Tjonna, at which “you cannot talk in full
sentences, but can use single words” — for four four-minute intervals,
with three minutes of slow walking between, followed by a brief
cool-down. The entire session was repeated three times a week for 10
weeks.

The second group, however, completed only one four-minute strenuous run. They, too, exercised three times a week for 10 weeks.

At
the end of the program, the men had increased their maximal oxygen
uptake, or endurance capacity, by an average of 10 percent or more, with
no significant differences in the gains between the two groups.